Power switches, such as field effect transistors, are widely used in a variety of circuits and a variety of devices. An ideal power switch would be capable of switching on immediately when instructed to do so by a control signal. However, real world devices are not ideal, and thus there is a delay between receipt of the control signal by the power switch and the actual turning on of the switch. The converse is true with respect to the turning off of the power switch.
The delay in the switching operation of the power switch imposes a constraint on the switching frequency and duty cycle of power switch. During the switching of the power switch, the voltage slew rate of the switching node should be controlled to improve EMI (Electro Magnetic Interference) behavior so as to not disturb operation of other portions of an electronic device incorporating the power switch. For a low side driving power switch, the switching node is drain of the power switch. For a high side driving power switch, the switching node is the source of the power switch. If the slew rate of the switch node is fast, an undesirable amount of EMI is generated. However, if the slew rate of the switch node is slow, the efficiency of the power switch is low since power consumption during switching is high.
Therefore, a need exists for a driving circuit for a power switch that can carefully and precisely control the slew rate of the switch node.